The time of bolting is an important factor in lettuce production because it affects the yield and quality of the harvested crop. Bolting is promoted by higher temperatures and is an increasing problem for growers with the current trend for warmer summers. Lettuce plants that are in the early stages of bolting are visibly indistinguishable from non-bolting plants, however there are changes in the biosynthesis of secondary metabolites which are produced to protect the young floral bud from insect attack. These compounds give the lettuce plant a bitter taste and render the crop unsaleable. The development of late bolting varieties, which would have a greater ‘holding ability’ in the field, would result in reduced crop losses and an extension to the growing season. In many plants, the timing of the transition from vegetative growth to flowering is controlled by environmental cues which serve to communicate growth conditions favourable for sexual reproduction and seed maturation. Studies in Arabidopsis have led to the identification of several different pathways that come together to regulate flowering time. Little research has been done on these response pathways in lettuce, however, research has shown that components of these pathways are conserved between Arabidopsis and other crop species. The aim of this project is to isolate genes regulating flowering time in lettuce in order that novel alleles of these genes can be used to manipulate bolting time. A lettuce BAC library has been screened and homologues of eight Arabidopsis flowering time genes, principally from the autonomous pathway, have been isolated. Functional orthologues of FLOWERING LOCUS T (FT) and the autonomous pathway gene, FLK have been characterised in lettuce, suggesting that there is conservation of the genes involved in flowering time in Arabidopsis and lettuce. Lettuce lines with a range of bolting times, including lines which bolt significantly later than wild-type have been identified from EMS mutagenised populations of cultivated lettuce and a diversity set of wild lettuce. Homozygous lines from a Lactuca sativa cv. Larissa EMS population with a reproducible late bolting phenotype when tested under commercial growing conditions have been identified. These lines have been made available to Rijk Zwaan® for inclusion in future breeding programs aimed at delaying bolting and improving the ‘holding’ ability’ of commercial lettuce crops. Genomic sequence of selected lettuce flowering time genes have been compared between the late bolting lines and wild-type looking for polymorphisms that may account for the late bolting phenotype. Polymorphisms within these genes were identified in some of the late bolting lines, however through analysing the polymorphism in segregating backcross populations they have been shown not to be causing the late bolting phenotype. Transcriptome sequencing has also been performed to identify polymorphisms in other, possibly novel, genes which may be causing the late bolting phenotype, as yet, no mutation segregating within the late bolting lines has been identified.

Supervisor:

Not available

Sponsor:

Biotechnology and Biological Sciences Research Council (Great Britain) (BBSRC)